I have Intel D850MV motherboard with two 256 MB and two 128 MB RDRAMs, AGP video card with 128 MB on-board RAM, Samsung 40 GB HDD (ATA) and DVD R/RW drive. Upon plugging the computer to the power source it powers up before the power button is pressed. The power LED, HDD indicator LED and two LEDs on the motherboard light up. The cooling fans on the processor and inside SMPS start rotating.
But there is no activity and no display on the monitor. There are no beeps. The power switch and the reset switch do not function. However if power switch is kept pressed the computer shuts down. The CPU and video card heat sink and hard disk become warm. The DVD LED lights up initially and drive door can be opened and closed.

What could be the problem? I am located reasonably far from authorized service outlets. Any advice useful for my local service person will be most welcome.

Meanwhile, try this.

With your computer off, reset the cmos. Refer to your motherboard manual on how to clear or reset the cmos.

Or by pulling the cmos battery out on the motherboard for an hour or more then put it back again to its battery holder. Start your computer.